Saturday, December 18, 2010

Paper: Arctic Temperatures 2-3C higher only 1000 years ago

A paper presented at the American Geophysical Union meeting this week finds that Ellesmere Island in the Canadian High Arctic experienced a "dramatic" Medieval Warming Period from 800-1200 AD with temperatures 2 to 3 degrees C higher than the mean temperature of the past 100 years. Ellesmere Island was also in the news this week due to a discovery of a mummified forest where "no trees now grow" due to its "current frigid state."

A 5,000 year alkenone-based temperature record from Lower Murray Lake reveals a distinct Medieval Warm Period in the Canadian High Arctic

Lake-based paleotemperature reconstructions are of particular importance in the Arctic, where other useful archives (e.g., tree rings, speleothems) for developing dense networks of quantitative climate records are absent or limited. Lacustrine alkenone paleothermometry offers a new avenue for investigating the evolution and variability of Arctic temperatures during the Holocene. We have generated a ~5,000 year long, decadally-resolved record of summer water temperature from the annually-laminated sediments of Lower Murray Lake on Ellesmere Island in the Canadian High Arctic. The varved sediments of Lower Murray Lake allowed high-resolution sampling and excellent chronologic control of the sedimentary record. We calibrated the alkenone paleothermometer for Lower Murray Lake using previously published data as well as new data from lakes in Norway and Svalbard, providing a quantitative record of temperature variability for the past 5,000 years. The previously published mass accumulation rate from Lower Murray Lake has been interpreted as a paleotemperature record and provides complimentary information to the new alkenone record. Melt percentage measurements from the nearby Agassiz Ice Cap provide another independent summer temperature reconstruction for comparison. Most strikingly, the alkenone record reveals warm lake water temperatures beginning ~800 AD and persisting until ~1200 AD, with temperatures up to 2-3 deg C warmer than the mean temperature for the past 100 years. This dramatic medieval warm period on Ellesmere Island interrupted a distinct (neoglacial) cooling trend that had begun approximately 2000 years earlier. Furthermore, the three warmest intervals seen in the alkenone record during the past 5,000 years correspond to the periods during which the area was occupied by Paleo-Eskimo groups, providing evidence that local climate conditions played a significant role in determining migration patterns of people of the Arctic Small Tools tradition.

AP Dec 16, 2010: "On a remote island in the Canadian Arctic where no trees now grow, a newly unearthed mummified forest is giving researchers a peek into how plants reacted to ancient climate change.

That knowledge will be key as scientists begin to tease out the impacts of global warming in the Arctic.

The ancient forest found on Ellesmere Island, which lies north of the Arctic Circle in Canada, contained dried out birch, larch, spruce and pine trees. Research scientist Joel Barker of Ohio State University discovered it by chance while camping in 2009.

"At one point I crested a small ridge and the cliff face below me was just riddled with wood," he recalled.

Armed with a research grant, Barker returned this past summer to explore the site, which was buried by an avalanche 2 million to 8 million years ago. Melting snow recently exposed the preserved remains of tree trunks, leaves and needles.

About a dozen such frozen forests exist in the Canadian Arctic, but the newest site is farthest north.

The forest existed during a time when the Arctic climate shifted from being warmer than it is today to its current frigid state. Judging by the lack of diverse wood species and the trees' small leaves, the team suspected that plants at the site struggled to survive the rapid change from deciduous forest to evergreen.

"This community was just hanging on," said Barker, who presented his findings Thursday at the American Geophysical Union meeting in San Francisco.

The next step is to examine tree rings to better understand how past climate conditions stressed plant life and how the Arctic tundra ecosystem will respond to global warming.

Since 1970, temperatures have climbed more than 4.5 degrees in much of the Arctic, much faster than the global average."

1 comment:

Possibly the higher range of 3 C warmer. Trees will not survive if they don't get sufficient sunlight and warmth. With the coming new little ice age, perhaps scientists should mark and label hundreds of trees in the Arctic, if any, as they will be mummified again. Then scientists 500 or 1,000 yrs from now will discover those trees labelled this year or next year. And they can draw more data and conclusions of our current climate compared to their current (our future) climate.